dpkg: Store Multi-Arch field in update log for newly installed packages

This is needed to be able to find the correct slot where the package
entry instance from the update log should be inserted to, specially
when dealing with architecture cross-gradings.

src/processarc.c

@@ -748,8 +748,10 @@ void process_archive(const char *filename) {
   }
 
   pkg_set_eflags(pkg, eflag_reinstreq);
-  if (pkg->status == stat_notinstalled)
+  if (pkg->status == stat_notinstalled) {
     pkg->installed.version= pkg->available.version;
+    pkg->installed.multiarch = pkg->available.multiarch;
+  }
   pkg_set_status(pkg, stat_halfinstalled);
   modstatdb_note(pkg);
   if (oldversionstatus == stat_notinstalled) {